1. Field of the Invention
The present invention generally relates to a conveying device conveying a recording medium, such as a recording sheet, on which an image is printed by jetting a liquid such as an ink thereto, a conveyance control device, and an inkjet recording device printing such an image on the recording medium, and more particularly, to a conveying device which can convey the recording medium with high precision so as to increase a positional precision of applying the liquid onto the recording medium to stably form a high-quality image on the recording medium.
2. Description of the Related Art
A full-colored image can be formed by an electrophotographic method including steps of forming an electrostatic latent image on a photosensitive member, developing each color, and then overlapping the developed colors. However, in performing this method, the step of overlapping the colors is difficult. Further, the method involves complicated component devices including developing devices around the photosensitive member, which enlarges an image-forming device as a whole, and increases costs thereof. By contrast, with an inkjet recording device printing on a recording sheet by jetting ink drops thereon, it is easy to overlap the colors. Additionally, the inkjet recording device has a small recording head jetting the ink drops, which reduces the size of the image-forming device as a whole. Also, the inkjet recording device is excellent in terms of a photographic quality. Further, an image formed on an OHP by the inkjet recording device has an excellent optical transmittance.
In pursuit of a higher-quality image in this inkjet recording device, the ink drops need to be jetted to landing spots on the recording sheet with higher precision. Therefor, not only the recording head jetting the ink drops needs to be further sophisticated in structure, but also the recording sheet needs to be conveyed with higher precision. In a serial printer of an inkjet type, the recording sheet is stopped while the recording head performs a scanning. Accordingly, the recording sheet is repeatedly conveyed and stopped. At this point, a precision of conveying the recording sheet means conveying the recording sheet a predetermined distance, and thereafter stopping the recording sheet at a predetermined position.
For the purpose of enhancing the precision of conveying the recording sheet, in inkjet recording devices disclosed in Japanese Laid-Open Patent Application No. 4-201469, Japanese Laid-Open Patent Application No. 9-254460, and Japanese Laid-Open Patent Application No. 2000-25249, for example, a conveying belt conveying the recording sheet is uniformly charged positively so that the recording sheet is stick fast to the conveying belt by an electrostatic force so as to prevent the recording sheet from being displaced. However, in this state, the ink drops jetted from the recording head are influenced by an electric field such that landing spots of the ink drops are displaced on the recording sheet. For the purpose of preventing this displacement of the landing spots of the ink drops, a negative charge is applied to the conveying belt uniformly charged positively on the surface, in the vicinity of the recording head so as to lessen the electrostatic force so that the ink drops jetted from the recording head are not influenced by the electric field, as described in Japanese Laid-Open Patent Application No. 2000-25249, for example. Additionally, as described in Japanese Laid-Open Patent Application No. 4-201469, for example, a circumferential groove is formed at a predetermined position in an axial direction of a conveying roller, and a projection is formed at a position in a widthwise direction of the conveying belt wound around the conveying roller, the position corresponding to the circumferential groove of the conveying roller, wherein the projection of the conveying belt is engaged in the circumferential groove of the conveying roller so as to regulate the widthwise position of the conveying belt.
However, applying the negative charge, as mentioned above, to the conveying belt in the vicinity of the recording head so as to lessen the electrostatic force necessitates a means therefor, which disadvantageously complicates an entire structure of a conveying device conveying the recording sheet. Additionally, after an image is recorded on the recording sheet by jetting the ink drops thereon, separating the recording sheet from the conveying belt necessitates a separating force that exceeds the electrostatic force applied throughout the surface of the recording sheet, which makes it difficult to provide a separating unit capable of separating the recording sheet. Further, when the conveying belt slips on the conveying roller, the recording sheet is displaced in a direction in which the recording sheet is conveyed by the conveying belt, reducing the precision of conveying the recording sheet.
Additionally, when an image is recorded on the recording sheet by jetting the ink drops thereon, the recording sheet is elongated due to water contained in the ink drops. This phenomenon is referred to as a cockling. Due to this cockling, the recording sheet becomes wavery such that the distance between nozzles of the recording head and the surface of the recording sheet varies depending on the position. When this cockling becomes aggravated, the recording sheet contacts the nozzles of the recording head, at worst, such that the nozzles of the recording head become dirty, and that the recording sheet is smeared. Further, this cockling may displace the landing spots of the ink drops on the recording sheet. In order to prevent these influences of the cockling, an image is formed on a recessed platen by jetting the ink drops from the recording head thereon, while the recording sheet is pressed by a spur having projections on its periphery. However, pressing the recording sheet by the spur may leave a scar on the image formed on the recording sheet, resulting in a deterioration of the image. Also, in order to prevent the above-mentioned influences of the cockling, there is another measure as described in Japanese Laid-Open Patent Application No. 2000-191175. According to this measure, protruding parts and recessing parts are formed on the surface of the conveying belt. The recessing parts are provided with air inflow ports. Vacuum suction is performed via these air inflow ports so as to vacuum-suck the recording sheet to the conveying belt. Thereby, the waves occurring in the recording sheet undergoing the above-mentioned cockling are made lower such that the recording sheet does not contact the recording head.
However, when the recording sheet is vacuum-sucked by the recessing parts of the conveying belt so as to prevent the above-mentioned influences of the cockling of the recording sheet, the recording sheet in the vicinity of the recording head also becomes uneven according to the protruding parts and recessing parts formed on the surface of the conveying belt. This unevenness on the recording sheet displaces the landing spots of the ink drops on the recording sheet, which results in a deteriorated image.
Further, there is also an inkjet recording device comprising a pair of conveying rollers, one of the pair being a combination of the above-mentioned spur and a roller, in which the pair of the conveying rollers convey the recording sheet. In this device, the precision of conveying the recording sheet can be guaranteed only when the recording sheet engages the pair of the conveying rollers. In recent years, there has been a need for an expansion of an image printing area. For the purpose of securing this printing area, there is also an inkjet recording device forming an image in a state that cannot essentially guarantee the precision of conveying the recording sheet, i.e., in a state where the recording sheet engages only either of the pair of the conveying rollers. When an elevation of the recording sheet occurs in this state, the inkjet recording device is unable to deal with this elevation, and cannot secure a force for conveying the recording sheet; thereby, the precision of conveying the recording sheet cannot be guaranteed, and a quality of an image is reduced.
It is a general object of the present invention to provide an improved and useful recording-medium conveying device, a conveyance control device, and an inkjet recording device, in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a recording-medium conveying device, a conveyance control device, and an inkjet recording device, which can enhance a precision of conveying a recording sheet with a simple configuration, and can expand an printing area of the recording sheet while stably forming a high-quality image.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a recording-medium conveying device conveying a recording medium to an image recording part, the recording medium being separated and fed from a recording-medium feeding device, the recording-medium conveying device comprising:
a conveying belt wound around a driving roller and a driven roller so as to convey the recording medium to the image recording part, the conveying belt having an insulating layer formed at at least a side contacting the recording medium; and
a belt charging unit provided in contact with the conveying belt so as to charge the conveying belt with a positive charge and a negative charge alternately in a moving direction of the conveying belt by applying an AC bias to the conveying belt.
According to the present invention, a micro electric field is induced from the positive charge to the negative charge charged in the conveying belt. This micro electric field causes the recording medium to stick fast electrostatically to the conveying belt. Accordingly, the recording medium can be stably conveyed to the image recording part. Additionally, the recording medium can be conveyed while the evenness of a print surface thereof is maintained without being pressed by a spur, etc. Therefore, not only a high-quality image can be stably formed on the recording medium, but also the print surface of the recording medium can be prevented from being smeared or damaged.
Additionally, in the recording-medium conveying device according to the present invention, the belt charging unit may preferably apply the AC bias to the conveying belt while the conveying belt conveys the recording medium, and the belt charging unit may preferably stop applying the AC bias to the conveying belt while the conveying belt stops conveying the recording medium.
According to the present invention, this function of stopping the application of the AC bias prevents the AC bias from removing the charges charged in the conveying belt, and also prevents charges from being charged in unintended directions.
Additionally, in the recording-medium conveying device according to the present invention, the belt charging unit may apply the AC bias to the conveying belt while the conveying belt is continuously revolved, before the conveying belt conveys the recording medium.
According to the present invention, the positive charge and the negative charge can be stably charged in the conveying belt.
Additionally, in the recording-medium conveying device according to the present invention, the conveying belt may be formed of one layer of the insulating layer, or may be formed of two layers composed of the insulating layer formed at one side contacting the recording medium and a conductive layer formed at the other side not contacting the recording medium.
According to the present invention, the positive charge and the negative charge charged by applying the AC bias can be stably retained in the insulating layer of the conveying belt.
Additionally, in the recording-medium conveying device according to the present invention, the insulating layer may have a volume resistivity equal to or more than 1012 xcexa9cm, preferably 1015 xcexa9cm.
According to the present invention, the positive charge and the negative charge alternately charged in the insulating layer are prevented from moving across boundaries therebetween so that the insulating layer can be charged stably with the positive charge and the negative charge alternately.
Additionally, the recording-medium conveying device according to the present invention may further comprise conveyance guides provided at both sides of the conveying belt in a widthwise direction thereof so as to guide the recording medium, the conveying belt being formed narrower than the recording medium.
According to the present invention, the conveyance guides prevent an elevation of the recording medium soaking the ink drops, and thereby prevents a displacement of landing spots of the ink drops on the recording medium.
Additionally, in the recording-medium conveying device according to the present invention, the conveyance guides may comprise a plurality of ribs and recession grooves alternately, each of the ribs and the recession grooves being aligned along a conveying direction of the recording medium.
According to the present invention, parts of the elongated recording medium soaking the ink drops sag into the recession grooves where the ribs do not exist. This prevents an elevation of the recording medium soaking the ink drops.
Additionally, the recording-medium conveying device according to the present invention may further comprise a pressing roller pressing the conveying belt against the driving roller by exerting an elastic force so as to prevent the conveying belt from slipping on the driving roller.
According to the present invention, not only the conveying belt is prevented from slipping on the driving roller, the recording medium stuck electrostatically to the conveying belt can be pressed closely against the conveying belt 214 so that the recording medium adheres further firmly to the conveying belt electrostatically.
Additionally, in the recording-medium conveying device according to the present invention, the pressing roller may be provided at a position downstream in a revolving direction of the driving roller.
According to the present invention, the recording medium can be surely stuck fast to the conveying belt at the image recording part including a recording head so as to be conveyed with higher precision.
Additionally, in the recording-medium conveying device according to the present invention, at least the driving roller among the driving roller and the driven roller may have a plurality of projections on a surface thereof. Preferably, the conveying belt may be formed of a timing belt.
According to the present invention, the conveying belt can be more surely prevented from slipping on the driving roller or the driven roller.
In order to achieve the above-mentioned objects, there is also provided according to another aspect of the present invention a recording-medium conveying device conveying a recording medium to an image recording part, the recording medium being separated and fed from a recording-medium feeding device by a separating unit thereof, the recording-medium conveying device comprising:
a conveying belt wound around a driving roller and a driven roller so as to convey the recording medium to the image recording part, the conveying belt having a two-layer structure composed of an insulating layer formed at one side contacting the recording medium and a conductive layer formed at the other side not contacting the recording medium;
a belt charging unit provided in contact with the insulating layer in a vicinity of the separating unit so as to charge the insulating layer with a positive charge and a negative charge alternately in a moving direction of the conveying belt by applying an AC bias to the conveying belt; and
a pressing roller pressing the conveying belt against the driving roller by exerting an elastic force so as to prevent the conveying belt from slipping on the driving roller.
In order to achieve the above-mentioned objects, there is also provided according to another aspect of the present invention a recording-medium conveying device conveying a recording medium to an image recording part, the recording medium being separated and fed from a recording-medium feeding device by a separating unit thereof, the recording-medium conveying device comprising:
a conveying belt wound around a central part of a driving roller and a central part of a driven roller so as to convey the recording medium to the image recording part, the conveying belt being narrower than the recording medium, and having a two-layer structure composed of an insulating layer formed at one side contacting the recording medium and a conductive layer formed at the other side not contacting the recording medium;
conveyance guides provided at both sides of the conveying belt in a widthwise direction thereof in the image recording part, the conveyance guides having a plurality of ribs and recession grooves alternately, each of the ribs and the recession grooves being aligned along a conveying direction of the recording medium;
a belt charging unit provided in contact with the insulating layer in a vicinity of the separating unit so as to charge the insulating layer with a positive charge and a negative charge alternately in a moving direction of the conveying belt by applying an AC bias to the conveying belt; and
a pressing roller pressing the conveying belt against the driving roller by exerting an elastic force so as to prevent the conveying belt from slipping on the driving roller.
Additionally, in the recording-medium conveying device according to the present invention, a surface of the driving roller may be cured, for example, by being coated with urethane.
In order to achieve the above-mentioned objects, there is also provided according to another aspect of the present invention a recording-medium conveying device conveying a recording medium to an image recording part, the recording medium being separated and fed from a recording-medium feeding device by a separating unit thereof, the recording-medium conveying device comprising:
a conveying belt wound around a driving roller and a driven roller so as to convey the recording medium to the image recording part, the conveying belt having a two-layer structure composed of an insulating layer formed at one side contacting the recording medium and a conductive layer formed at the other side not contacting the recording medium; and
a belt charging unit provided in contact with the insulating layer in a vicinity of the separating unit so as to charge the insulating layer with a positive charge and a negative charge alternately in a moving direction of the conveying belt by applying an AC bias to the conveying belt,
wherein at least one of the driving roller and the driven roller is a grip roller having a plurality of projections.
In order to achieve the above-mentioned objects, there is also provided according to another aspect of the present invention a recording-medium conveying device conveying a recording medium to an image recording part, the recording medium being separated and fed from a recording-medium feeding device by a separating unit thereof, the recording-medium conveying device comprising:
a conveying belt wound around a central part of a driving roller and a central part of a driven roller so as to convey the recording medium to the image recording part, the conveying belt being narrower than the recording medium, and having a two-layer structure composed of an insulating layer formed at one side contacting the recording medium and a conductive layer formed at the other side not contacting the recording medium;
conveyance guides provided at both sides of the conveying belt in a widthwise direction thereof in the image recording part, the conveyance guides having a plurality of ribs and recession grooves alternately, each of the ribs and the recession grooves being aligned along a conveying direction of the recording medium; and
a belt charging unit provided in contact with the insulating layer in a vicinity of the separating unit so as to charge the insulating layer with a positive charge and a negative charge alternately in a moving direction of the conveying belt by applying an AC bias to the conveying belt,
wherein at least one of the driving roller and the driven roller is a grip roller having a plurality of projections.
In order to achieve the above-mentioned objects, there is also provided according to another aspect of the present invention a recording-medium conveying device conveying a recording medium to an image recording part, the recording medium being separated and fed from a recording-medium feeding device by a separating unit thereof, the recording-medium conveying device comprising:
a conveying belt wound around a driving roller and a driven roller so as to convey the recording medium to the image recording part, the conveying belt having a two-layer structure composed of an insulating layer formed at one side contacting the recording medium and a timing belt formed by a conductive layer at the other side not contacting the recording medium; and
a belt charging unit provided in contact with the insulating layer in a vicinity of the separating unit so as to charge the insulating layer with a positive charge and a negative charge alternately in a moving direction of the conveying belt by applying an AC bias to the conveying belt.
In order to achieve the above-mentioned objects, there is also provided according to another aspect of the present invention a recording medium to an image recording part, the recording medium being separated and fed from a recording-medium feeding device by a separating unit thereof, the recording-medium conveying device comprising:
a conveying belt wound around a central part of a driving roller and a central part of a driven roller so as to convey the recording medium to the image recording part, the conveying belt being narrower than the recording medium, and having a two-layer structure composed of an insulating layer formed at one side contacting the recording medium and a timing belt formed by a conductive layer at the other side not contacting the recording medium; and
conveyance guides provided at both sides of the conveying belt in a widthwise direction thereof in the image recording part, the conveyance guides having a plurality of ribs and recession grooves alternately, each of the ribs and the recession grooves being aligned along a conveying direction of the recording medium; and
a belt charging unit provided in contact with the insulating layer in a vicinity of the separating unit so as to charge the insulating layer with a positive charge and a negative charge alternately in a moving direction of the conveying belt by applying an AC bias to the conveying belt.
Additionally, in the recording-medium conveying device according to the present invention, the timing belt may be formed at at least a part of the other side of the conveying belt.
Additionally, in the recording-medium conveying device according to the present invention, one of the driving roller and the driven roller positioned upstream in the conveying direction of the recording medium may have a large diameter, and the other of the driving roller and the driven roller positioned downstream in the conveying direction of the recording medium may have a small diameter.
In order to achieve the above-mentioned objects, there is also provided according to another aspect of the present invention a recording-medium conveying device conveying a recording medium to an image recording part, the recording medium being separated and fed from a recording-medium feeding device, the recording-medium conveying device comprising:
a conveying belt wound around a driving roller and a driven roller, the driving roller being connected to a ground, so as to convey the recording medium to the image recording part, the conveying belt having an insulating layer formed at a side contacting the recording medium;
a belt charging unit provided opposite the driving roller at a position upstream in a revolving direction of the driving roller from a position at which the recording medium fed from the recording-medium feeding device contacts the conveying belt wound around the driving roller so as to charge the conveying belt with a positive charge and a negative charge alternately in a moving direction of the conveying belt by applying an AC bias to the conveying belt; and
a pressing roller provided opposite the driving roller at a position downstream in the revolving direction of the driving roller from the belt charging unit so as to press the recording medium stuck fast to the conveying belt closely to the conveying belt.
According to the present invention, the recording medium can be conveyed stably.
Additionally, in the recording-medium conveying device according to the present invention, the AC bias may impressed to the belt charging unit when the recording medium is conveyed. Further, the AC bias is preferred to be stopped being impressed to the belt charging unit when the recording medium is stopped being conveyed.
Alternatively, in the recording-medium conveying device according to the present invention, the AC bias may be impressed to the belt charging unit while the conveying belt is continuously revolved, before the recording medium is conveyed.
In order to achieve the above-mentioned objects, there is also provided according to another aspect of the present invention a conveyance control device controlling one of the above-mentioned recording-medium conveying devices, the conveyance control device comprising:
a binary scale provided on a part of the conveying belt along the moving direction thereof,
wherein one of a reflected light and a transmitted light from the binary scale is detected so as to control a revolving velocity and a stopping position of the driving roller.
Additionally, the conveyance control device according to the present invention may further comprise an optical sensor provided opposite a part of the conveying belt downstream from and near the driving roller so as to detect one of the reflected light and the transmitted light. Alternatively, the conveyance control device according to the present invention may further comprise an optical sensor provided opposite a part of the conveying belt corresponding to the image recording part so as to detect the reflected light.
In order to achieve the above-mentioned objects, there is also provided according to another aspect of the present invention a conveyance control device controlling one of the above-mentioned recording-medium conveying devices, the conveyance control device comprising:
a conveyance distance detecting unit detecting one of a conveyance speed and a conveyance distance of the conveying belt; and
a conveying-belt driving unit driving the driving roller,
wherein the conveying-belt driving unit is controlled according to one of the conveyance speed and the conveyance distance detected by the conveyance distance detecting unit.
According to the present invention, the recording medium can be conveyed at a conveyance speed optimum for an image formation.
Additionally, in the conveyance control device according to the present invention, the conveyance distance detecting unit may comprise:
a binary scale provided on one of an outer surface and an inner surface of the conveying belt; and
a read sensor reading the binary scale,
wherein the binary scale has pitches arranged at an interval corresponding to a value obtained by dividing a maximum resolution of an image to be recorded on the recording medium by n, where n is an integer larger than zero.
Additionally, in the conveyance control device according to the present invention, the conveyance distance detecting unit may comprise an encoder provided on a rotary shaft of the driving roller,
wherein the driving roller has a diameter determined such that a conveyance distance of the conveying belt corresponding to one pulse output by the encoder becomes a value obtained by dividing a maximum resolution of an image to be recorded on the recording medium by n, where n is an integer larger than zero.
According to the present invention, the feed distance (the conveyance distance) of the conveying belt electrostatically absorbing the recording medium can be controlled according to a unit distance corresponding to the maximum resolution. Accordingly, in an inkjet printer of a serial type, a precision of starting a new print line can be controlled with high precision, and in an inkjet printer of a line type, a speed of starting a new print line can be controlled with high precision. Therefore, a high-quality image can be stably formed on the recording medium.
In order to achieve the above-mentioned objects, there is also provided according to another aspect of the present invention an inkjet recording device comprising:
a recording head (mounted on a carriage) in an image recording part so as to record an image by jetting ink drops on a recording medium;
a recording-medium feeding device containing the recording medium, and separating and feeding the recording medium one by one therefrom by a separating unit thereof; and
one of the above-mentioned recording-medium conveying devices.
In order to achieve the above-mentioned objects, there is also provided according to another aspect of the present invention an inkjet recording device comprising:
a recording head mounted on a carriage in an image recording part so as to record an image by jetting ink drops on a recording medium;
a recording-medium feeding device containing the recording medium, and separating and feeding the recording medium one by one therefrom; and
one of the above-mentioned recording-medium conveying devices.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.